The goal of this project is to increase our understanding of brain function and development in autism. Hypotheses regarding the neurobiological basis of autism will be tested by exaining whether individual differences in early symptom expression in autism are related to performance on neuropsychological tasks that are known to be mediated by different brain regions, and to patterns of functional brain imaging. The longitudinal stability of neuropsychological profile in children with autism from early preschool to elementary school age will mental retardation and typical development will participate in these studies, which address the following aims: Aim 1 is to identify specific neuropsychological impairments in young children with autism. Tasks known to be mediated by the dorsolateral prefontal, parietal, medial temporal, or cerebellar brain regions will be administered to young children with autism and matched comparison children, and relations between neuropsychological performance and severity of autistic symptoms will be examined. Aim 2 is to utilize high-density ERP brain imaging to study the morphology and spatial localization of brain electrical activity during the recognition of familiar faces and the discrimination of emotional expressions. Studies have linked face recognition and emotion perception to the medial temporal lobe. This project will examine the presence and universality of these impairments in autism, as well as their neural correlates. Aim 3 is to examine the stability of neuropsychological profile in children with autism and mental retardation from early preschool to elementary school age. Children will be followed longitudinally and be administered a comprehensive neuropsychological battery at 6-7 years of age. Aim 4 is to investigate early-emerging behavioral impairments in autism. Studies have been designed to shed light on impairments in orienting to social stimuli, motor imitation, joint attention, responses to emotional stimuli, symbolic play, and precursors to a "theory of mind." The results of these studies will address specific hypotheses regarding the nature of these early behaviornal impairments and allow for systematic investigation of the relation between autistic symptoms and brain function.